A control apparatus which controls the surface grinding of a plurality of substantially like workpieces to a predetermined accuracy in a precision grinding machine, which has a plurality of spindles with a workpiece receiving component and a workpiece mount in a switchable spindle head, is known.
This control apparatus comprises a measuring sensor and an electronic measuring unit, with which the measuring sensor determines the actual height value of the workpiece blank to be worked on the workpiece mount relative to a reference point on the appropriate spindle. The actual height value is fed to the measuring unit. The measuring unit controls the surface grinding considering the actual height value.
The workpiece blank can be metal, hard metal, ceramic material and/or plastic material. The workpiece blanks have tolerance-dependent thickness variations. They must be ground exactly within narrow tolerances and simultaneously are brought to a predetermined thickness.
"Switchable" in regard to the spindle heads means that the spindles on it are moved in the operating cycle from a loading station past a measuring station and one or more processing (grinding) stations of the unloading station. Generally the spindles rotate with the workpiece receiving components (seats, collets or chucks).
In the current control process used in practice and on which the invention is based, the workpiece receiving components and thus their mounts are carefully set up so that the surface of the workpiece receiving components, i.e. the workpiece mounts, seats, chucks or collets have a predetermined spacing relative to the reference point on the spindle which is equal for all spindles and is considered equal by the measuring unit from spindle to spindle. Consequently the grinding tool can be controlled in operation according to the actual height value relative to the reference point to adjust the workpiece to a predetermined thickness.
In fact the principal replaceable workpiece receiving components are very unequal because of basic tolerances even if they are made with the utmost care. These height precision variations are not considered in the current control process and lead to thickness errors in the worked workpiece. If the workpiece receiving component is higher than the constant value of its height stored or fed to the measuring unit, then the workpiece is made too thin. In the reverse situation it is too thick, i.e. when the workpiece receiving component is lower than the corresponding constant value.